Lime-burning process



Jm 16, 192s. n l-y WARN ER LIME BURNING PROCESS Filsd Sept. 15, 1923 Patented June 16, 1925.

UNITED STATES IRVING WARNER, 0F BELLEFONTE, PENNSYLVANIA.

LIME-BURNING PROCESS.

Application led September 15, 1923. Serial N'o. 662,954.

To all whom t may concer/n.'

Be it known that I, IRVING WARNER, a

citizen of the United States, residing atl Bellefonte, in the county of Center and State of Pennsylvania, have invented certain new and useful Improvements in Lime- Burning Processes, of which the following is a specification.

This invention relates to a lime burning process particularly adapted to be employed in connection with a rotary kiln and to apparatus for carrying out the process.

As is well known in the art, the' use of a rotary kiln in the burning of lime is open to the objection that it 1s difficult, if not impossible, to secure a complete burning ofthe lime. Due to the inherent tendency of the smaller stone in the rolling mass to gather at the center, the larger stones pre.- vent the heat from contacting with the small stones. By grading the limestone so that the largest stone shall not be more than 2 or 21/2 times the size of the smallest stone i-mproved results are obtained, but this method of operation results in a loss of valuable raw material. .By limiting the thickness of the layer of stone in the kiln, more complete calcination is obtained, but this method results in a loss in capacity and eiiiciency of the kiln. While these methods or a combination of the methods may partially overcome the difficulty of imperfect calcination they are open to the serious objection that they add materially to the cost of production.

An object of the invention is to provide an economic process for obtaining completely Latent heat of decomposition of CO2 calcined lime, and more specifically to prov1de a process in-which a rotary kiln may be employed in the normal manner for performing one step of the process. The invention also contemplates the provision of appropriate apparatus in which the process may be performed.

According to current practice, the incompletely burned lime is cooled as rapidly as possible after its discharge from the rotary kiln, but vin carrying out my process the hot mixture of burned and unburned lime is stored for an appreciable time in a heatinsulated receptacle. In the storage or seasoning receptacle the unburned lime is raised to or above the decomposition temperature as the entire mass assumes a uniform temperature. -The transfer of heat readily takes place since the pieces containing unburned lime or core,7 i. e. showing the presence of CO2, are quite small and are evenly distributed throughout the mass.

The average temperature of the lime discharged from a rotary kiln is usually about 500 to 800 F. above the temperature of dissociation and it is evident from a mathematical standpoint that this excess heat, when properly conserved, is sufficient to complete the`calcination of such quantities of unburned lime as may be produced in a heavily loaded kiln. The latent heat of dis sociation of CaCO, per pound of C()2 evolved, is 1754 B. t. u. and the specific heat of lime is .217, hence the excess temperature over the temperature of dissociation necessary to drive olf one per cent of CO2 is Specific heat of lime X 100 600 .217 100=13,020 B. t. u.

available from'e'ach 100 pounds of lime, and this heat, when transferred to the unburned lime, will evolve Even in a heavily loaded kiln and with a considerable range of size it is comparatively easy to burn down to a CO2 content of 4% to 8% but it is very dificult to make a more completely calcined product. From the gures given above it will be seen that the sensible heat of the lime will be sufficient to complete the calcination when the videdwith a kiln hood 2 in which the fuel nozzle 3 is located. These arts of the apparatus may be of any stan ard design and any of the usual fuelsy ma be employed. The heat insulated receptac e 4 is arranged below the kiln hood and the inlet' 5 of the receptacle is made as small as practical to prevent loss of heat by radiation vfrom the lime within the receptacle. The to and walls of the receptacle 4 are jackete with or formed of any suitable material of low thermal .conductivity to provide for the thorough insulation against heat losses. A suitable feeding out device, such as rotatin table 6 and an ad'ustable knife scraper may be employed or discharging the completely calcined lime from the seasoning receptacle. The hot lime removed by `the scraper 7 falls upon a chute 8 which conveys it toa cooler, such as a revolving cooler 9. Although the inlet opening of the receptacle is designed to prevent loss of heat by radiation and convection it is not essential that.

the outlet oponin be air tight, in fact the ingress of a smal quantity of air such as would normally takes place .with any feeding device of common use will be helpful in removing the CO2 evolved during the seasonin process.

he ca acity of the receptacle is preferably suc thatit Will hold about 4 hours output of the kiln butrseasoning for much shorter periods may be sufficient to complete the calcination and a seasoning of even one hour or a half-hour will greatl improve the product. The .discharge mec anism is so re ulated that the receptacle may be kept as fu l as possible at all tunes.

It is to be noted that the rocess does not contemplate a cooling of e mass Within the receptacle but is based upon a transfer of heat between unequally heated particles in a hi hly heated mass. So far as is possible,

lthe Y eat of the lime as it leaves the kiln is the object of maintaining the greatest mass 1gossible within the seasoning receptacle and eeping the material contained therein at substantially the same level. This will permit a seasoning receptacle of an given size to operate at its maximum e ciency and when the lime is removed from the bottom it may be cooled by any of the processes now employed for cooling the burnt lime as discharged directly from the kiln.

It will be understood that the invention is not limited to the specic apparatus which is shown in the drawings, since various forms of heat insulated receptacles and 'associated chutes or conveyors may be employed in carrying out the process.

While l have in the claims referred to a rotary kiln, my invention includes other like calcining means in which the limestone is subjected to calcining conditions like those in arotary kiln.

l claim:

The process of making lime from limestone which consists in heating the same in passage through a rotary kiln to a temperature above that of dissociation and then transferri the heated mass,'while still above the dissociation temperature. to a heat insulated receptacle and permitting the mass to remain in this receptaclefor a sufcient time to complete the calcination.

t In testimony whereof I aiiix my signaure.

InviNG WARNER. 

